The present invention relates to an image forming apparatus.
In a conventional image forming apparatus such as a printer, a copier, and a facsimile, an image is formed through the following process. First, a charge roller charges a surface of a photosensitive drum. An exposure device such as an LED head exposes the surface of the photosensitive drum to form a static latent image or a latent image thereon. A developing roller attaches a thin layer of toner to the static latent image to form a toner image. A transfer roller transfers the toner image to a recording medium, thereby forming an image. A cleaning device removes toner remaining on the photosensitive drum after the transfer roller transfers the toner image.
In the conventional image forming apparatus described above, when images are formed or a printing operation is performed continuously, each of the components such as the photosensitive drum, the charging roller, and the cleaning roller tends to wear. Accordingly, each of the components is integrated to be a unit component such as an image forming unit, so that the image forming unit attached to a main body of the image forming apparatus is detachable. With the configuration, it is possible to replace the image forming unit as a disposable part when life of the image forming unit is completed.
There can be a case that, after the image forming unit is manufactured, such an image forming unit is stored for a long period of time until the image forming unit is installed in a printer as a replacement to be used. In this case, an ingredient of the charging roller or the developing roller may be separated out at a contact point between the photosensitive drum and the charging roller or the developing roller. As a result, the ingredient may stick to a surface of the photosensitive drum, thereby smearing the photosensitive drum.
In order to prevent the photosensitive drum from smearing, a plastic film may be inserted between the photosensitive drum and the charging roller or the developing roller. When the image forming unit is installed in a printer, the plastic film is removed. However, in the conventional printer, when the plastic film is removed, the plastic film is pulled against friction between the photosensitive drum and the charging roller or the developing roller. Accordingly, static charge is generated between the photosensitive drum and the plastic film, and the generated charge may remain on the photosensitive drum.
If the generated charge remains on the photosensitive drum, it is difficult to charge the photosensitive drum uniformly due to the generated charge when the charge roller charges the photosensitive drum. As a result, an image defect such as a dark spot and a streak may occur upon printing, thereby deteriorating image quality. Further, if static discharge occurs between the photosensitive drum and an external environment, a toner image tends to be distorted when the transfer roller applies a transfer voltage, thereby deteriorating image quality.
In view of the problems described above, an object of the present invention is to provide an image forming apparatus, in which it is possible to solve the problems in the conventional printer and improve image quality.
Further objects and advantages of the invention will be apparent from the following description of the invention.